Hexagonal Boron Nitride: The Thinnest
Insulating Barrier to Microbial Corrosion
Govinda Chilkoor,
Sushma Priyanka Karanam,
Shane Star,
Namita Shrestha,
Rajesh K. Sani,
§
Venkata K.K. Upadhyayula,
Debjit Ghoshal,
Nikhil A. Koratkar,
#,
M. Meyyappan,
and Venkataramana Gadhamshetty*
,,
Civil and Environmental Engineering,
Materials and Metallurgical Engineering,
§
Chemical and Biological Engineering, and
Surface Engineering Research Center, South Dakota School of Mines and Technology, 501 E. Saint Joseph Boulevard, Rapid City,
South Dakota 57701, United States
Green Technologies and Environmental Economics Platform, Chemistry Department, Umea University, Umea, Sweden, 90187
Department of Chemical and Biological Engineering,
#
Department of Mechanical, Aerospace and Nuclear Engineering, and
Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590,
United States
Center for Nanotechnology, NASA Ames Research Center, Moett Field, Mountain View, California 94035, United States
*
S
Supporting Information
ABSTRACT: We report the use of a single layer of two-
dimensional hexagonal boron nitride (SL-hBN) as the
thinnest insulating barrier to microbial corrosion induced
by the sulfate-reducing bacteria Desulfovibrio alaskensis G20.
We used electrochemical methods to assess the corrosion
resistance of SL-hBN on copper against the eects of both
the planktonic and sessile forms of the sulfate-reducing
bacteria. Cyclic voltammetry results show that SL-hBN-Cu
is eective in suppressing corrosion eects of the
planktonic cells at potentials as high as 0.2 V (vs Ag/
AgCl). The peak anodic current for the SL-hBN coatings is
36 times lower than that of bare Cu. Linear polarization
resistance tests conrm that the SL-hBN coatings serve as a barrier against corrosive eects of the G20 biolm when
compared to bare Cu. The SL-hBN serves as an impermeable barrier to aggressive metabolites and oers 91% corrosion
inhibition eciency, which is comparable to much thicker commercial coatings such as polyaniline. In addition to
impermeability, the insulating nature of SL-hBN suppresses galvanic eects and improves its ability to combat microbial
corrosion.
KEYWORDS: 2D coatings, hexagonal boron nitride, microbial corrosion, sulfate-reducing bacteria
M
icrobially induced corrosion (MIC) results in an
unanticipated attack on metals in seemingly benign
environments and threatens a range of multi-billion-
dollar industries including aviation, surface transportation, and
water infrastructure.
1
MIC accounts for 2040% of the annual
corrosion costs including direct and indirect impacts, which
have been estimated to reach as high as $1 trillion.
2
MIC poses
a signicant nancial burden in the U.S. alone in the form of
total direct costs ($30 $50 billion/year),
3
biocide require-
ments ($1.2 billion/year),
4
and direct costs in oil and gas
industries ($2 billion/year).
5
The U.S. annually spends nearly
$6 billion to combat MIC eects of sulfate-reducing bacteria
(SRB) alone.
6
The SRBs secrete exopolymers on metal surfaces
and form a biolm to induce uniform corrosion or localized
pitting attack using one or more of the following mechanisms:
7
(i) disruption of passivating metal-oxide lms, (ii) altering
redox conditions at the metalsolution interface, (iii)
regeneration of the electron acceptors, (iv) production of
aggressive metabolites (e.g., suldes), and (v) depolarizing the
cathodic reactions.
Major corrosion mitigation practices including protective
coatings and impressed current cathodic protection tend to fail
under MIC conditions. For example, commercially available
polymer coatings (e.g., epoxy liners) are prone to biodegrada-
tion, and they exhibit poor adhesion toward metals under
aqueous conditions.
811
The thickness of commercial coatings
(501000 μm) can also disrupt the functionality (e.g.,
Received: August 31, 2017
Accepted: February 12, 2018
Published: February 12, 2018
Article
www.acsnano.org
Cite This: ACS Nano 2018, 12, 22422252
© 2018 American Chemical Society 2242 DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
Downloaded via BINGHAMTON UNIV STATE UNIV NEW YORK on April 20, 2023 at 17:59:56 (UTC).
See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
electrical conductivity, porosity, dimensional tolerances) of the
underlying metals. Furthermore, SRB can accelerate the
corrosion cells present under cathodic protection systems
through cathodic depolarization by consuming hydrogen.
Recent studies have demonstrated the corrosion resistance of
graphene-based materials
1,1215
under both abiotic and MIC
conditions. The graphene coatings exhibit excellent chemical
inertness, ductility, hydro phobicity, impermeability, and
strength. Screening-level life cycle analysis has demonstrated
environmental benets of graphene coatings compared to zinc
coatings, under both aggressive atmospheric corrosion
15
and
MIC con ditions.
16,17
However, the nanoscale defects in
graphene coatings serve as cathodic sites for capturing and
reducing terminal electron acceptors and simultaneously
aggravating galvanic corrosion of the underlying metals.
18
Unlike graphene, the 2D hexagonal boron nitrided (hBN) can
be obtained as an insulating coating to suppress the galvanic
eects. The 2D hBN materials have been reported to yield
high-performance coatings endowed with exceptional proper-
ties related to adhesion, barrier, impermeability, and
stability.
1821
The hBN-coated metals (e.g., Cu and steel)
show oxidation resistance against corrosive eects of high
temperatures (1100 °C)
22
and harsh chemicals.
18,23,24
2D hBN-
coated Cu has been shown to be an excellent barrier against
Gram-negative Escherichia coli.
19
In this paper, we explore the use of a single-layered hBN
coating as a thinnest insulating barrier to protect metals against
MIC eects of aggressive sulfate-reducing conditions. We use
Desulfovibrio alaskensis G20 as the model for the SRB and Cu as
a technologically relevant metal. This study provides insight
into the performance of 2D hBN coating against the MIC
eects of the G20 strain in the planktonic and sessile forms.
Here, we assess and quantify the long-term performance of 2D
hBN coating on a temporal scale that reects Cu/biolm
dynamics in corrosion cells that are continuously operated
under a fed-batch mode. A series of alternate current (AC)
electrochemical impedance spectroscopy (EIS) tests, direct
current (DC) electrochemical methods such as potentiody-
namic polarization, cyclic voltammetry (CV), and linear
polarization resistance, and imaging techniques have been
used to investigate the underlying mechanisms that enable the
2D hBN coatings to protect metals against harsh MIC
conditions. Finally, we demonstrate that the single-layered
hBN coatings suppress galvanic corrosion eects that are
typically encouraged by single-layered graphene (SLG) coat-
ings.
RESULTS AND DISCUSSION
Characterization of Atomic Layers of Hexagon al
Boron Nitride. The low-magni cation image in Figure 1a
Figure 1. SEM, optical image, TEM and Raman characterization of as grown single layer hBN (SL-hBN). (a) The line in lower magnication
SEM image (indicated with yellow arrow) represent a Cu grain boundary and the dark patches are the Cu domains. Scale bar: 100 μm. (b)
The smaller scale faint grey zones (indicated in red arrow) in higher magnication SEM image represent few layered hBN lms. Scale bar: 2
μm. (c) Optical image of SL-hBN (light indigo) transferred onto a SiO
2
/Si substrate (background color). Scale bar: 50 μm. (d) TEM image
showing sheets of SL-hBN. Scale bar: 50 nm. (e) TEM image of folded edge showing a single parallel line conrming the presence of SL-hBN.
Scale bar: 2 nm. (f) Selected area electron diraction pattern shows the crystalline and hexagonal nature of SL-hBN. (g) Typical Raman
spectra for SL-hBN.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2243
show a monolayer of conformal hBN coatings deposited over
Cu foils by chemical vapor deposition (CVD). The Cu grain
boundaries are indicated with yellow arrows and the copper
domains as dark patches (Figure 1a,b). The higher-magni ca-
tion image in Figure 1b shows a monolayer of SL-hBN with
large area on the Cu foil. The occasional faint gray zones
suggest the presence of bilayers in certain regions. To further
conrm the presence of the SL-hBN lm on Cu foil, the sample
was transferred onto the SiO
2
/Si substrate using a poly(methyl
methacrylate)-based transfer method. The light indigo shade in
Figure 1c indicates a monolayer of hBN, whereas the brown
patch indicates the underlying SiO
2
/Si substrate through a
topographical defect induced during the transfer. The trans-
mission electron microscopy (TEM) analysis reveals the
transparent, aggregated crystalline structure for the hBN
coating (Figure 1d). Furthermore, the TEM image shows a
folded edge with one line indicating the presence of a layer of
hBN (Figure 1e) on the copper foil with a corresponding
interlayer spacing of 3.3 Å. These values match the theoretical
estimates for distances between lattice planes for bulk hBN.
25
The selected area diraction measurement shown in the TEM
image conrm an atomic-scale chicken wire (hexagonal)
pattern of hBN on the SL-hBN-Cu (Figure 1f). Finally, the
Raman data for the Si/SiO
2
-transferred hBN lm analyzed with
Figure 2. SEM images after air annealing (200 °C, 8 h) for (a) Bare Cu showing 70% of oxidized surface (b) SL-hBN-Cu showing 30% of
oxidized surface. Note: White area indicates oxidized copper and red area indicates protected copper. SEM images after 30% H
2
O
2
exposure
(2 h) for (c) Bare Cu showing 71% of oxidized surface (d) SL-hBN-Cu showing 45% of oxidized surface. Note: Green area indicates oxidized
copper and gray area indicates protected copper. (e) Raman spectra of a transferred CVD hBN lm on SiO
2
/Si showing surface coverage of
1488 μm
2
for hBN (equivalent to 88% surface coverage). WITEC 300R Confocal Raman Imaging was used with a laser wavelength of 532
nm and 100× objective lens.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2244
the Lorentzian peak tting method
18
conrm the Raman peak
at 1370 cm
1
(Figure 1g) that matches a single layer of hBN
lm.
26
Identifying Inherent Defects in SL-hBN. We carried out
detailed oxidation experiments to identify the defect density of
SL-hBN coatings. The results from the oxidation experiments
are summarized here with further details below: (1) SL-hBN
coatings were able to protect the underlying copper substrates
in oxidizing environments; (2) SL-hBN coatings are charac-
terized by inherent defects; (3) Raman mapping tests
corroborate the specic degree of surface coverage oered by
the single layer of hBN coating. The oxidation experiments
were carried out by exposing the SL-hBN-Cu and bare Cu to
oxidizing environments induced by air annealing (200 °C, 8
h). Another set of oxidation experiments was carried out by
treating the samples with 30% H
2
O
2
for 2 h. The exposure
time determined from preliminary trials ensured aggressive
oxidizing environments without destroying the samples. Figure
2a,b presents the scanning electron microscopy (SEM) images
for the oxidized samples at the end of the air annealing
experiments (200 °C, 8 h). The oxidized surface is shown as
the white layer on the copper substrate (red background). A
quantitative analysis using ImageJ software revealed that the
percentage of oxidized area for SL-hBN-Cu and bare Cu was
30 and 70%, respectively. Exposure to H
2
O
2
revealed that
SL-hBN-Cu is susceptible to oxidation under aqueous
conditions (oxidized surface in green color and unaected
copper in gray color) (Figure 2d). The H
2
O
2
experiments
revealed that the SL-hBN-Cu and bare Cu were oxidized by
45 and 71%, respectively (Figure 2c,d). These results
indicate that defects due to grain boundaries and uncoalesced
grains (measured in terms of the % copper oxidation) aect the
surface coverage oered by the SL-hBN coatings.
We carried out additional Raman mapping tests after
transferring the lms of SL-hBN-Cu on SiO
2
/Si specimens
(exposed area 1431 μm
2
)(Figure 2e). The Raman mapping
results indicate that hBN coatings were characterized with a
coverage area of 88%. Considering this situation, the
enhanced performance of the hBN coatings (i.e.,lower
corrosion rates) is attributable to its insulating nature and its
resultant ability to repress galvanic eects (as discussed later).
Improving surface coverage is expected to further enhance the
ability of hBN coatings to combat MIC.
Crystallographic Orientation of Cu and the Eect on
Defects in SL-hBN. The hBN lms grown using the CVD
process are prone to intercalation of corrosion molecules due to
the following two factors: (i) defects that develop due to
discontinuous formation of layers in the form of isolated islands
or domains and (ii) mismatch of copper and hBN orientation
due to polycrystalline copper which introduces dierent
interfaces with hBN, allowing ions to intercalate between the
hBN lm and copper substrate.
2729
Based on previous studies,
the lowest defect density for hBN growth on copper requires
the Cu surface to have a [111] direction.
30,31
The single-crystal
orientation of Cu helps to match the hexagonal lattice of hBN
to produce high-quality and large-scale conformal coating. It
eliminates the presence of numerous small-sized grains and
grain boundaries which are sources of coating degradation and
Figure 3. Electrochemical data within 24 h of exposure to sessile SRB-G20 medium. (a) Potentiodynamic polarization and (b) cyclic
voltammetry curves for bare Cu and SL-hBN-Cu. (c) Optical images of Bare Cu and SL-hBN-Cu after destructive test. Scale: 20 μm.
Potentiodynamic polarization measurements in a potential range of 300 to +1000 mV from open-circuit voltage. Cyclic voltammetry
measurements in the potential window of 700 to +200 mV (vs Ag/AgCl) for bare Cu; for SL-hBN, positive potential was extended up to
+500 mV. (d) Nyquist plot of Bare-Cu and SL-hBN-Cu.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2245
increased defect density. The copper foils used for growing
hBN have unfavorable crystallographic orientation (Figure
S1a,b), which indicates that the as-grown hBN lms are also
expected to be characterized by defects. To further understand
the Cu grain orientations in SL-hBN-Cu, we carried out
electron backscattering diraction mapping (Figure S1b). The
mapping for SL-hBN (Figure S1b) was mono crystalline
Cu[100]. Future work should involve utilizing CVD substrates
with favorable crystallographic orientation in an eort to reduce
defects and improve the surface coverage of hBN coatings.
High-Performance, Nanoscale hBN Coatings for
Microbially Induced Corrosion Resistance. Sulfate-reduc-
ing bacteria represent a diverse group of prokaryotes that are
known to accelerate corrosion of technologically relevant
metals. We used D. vibrio G20 as the model for Gram-negative
mesophilic SRB to evaluate the MIC resistance of SL-hBN-
coated Cu using the following three experiments: (i) abiotic
control; (ii) planktonic cell test (G20 cells in suspension); and
(iii) biolm test (G20 cells encapsulated in a biological lm).
Biotic vs Abiotic Corrosion under Neutral Conditions. As
discussed in the Supporting Information (Figures S2 and S3),
the lactate C media did not exert any corrosive eects on Cu in
the absence of the G20 strain (i.e., abiotic conditions). For
example, the open-circuit potential (OCP) for the biotic tests
shifted to negative values (750 mV vs Ag/AgCl) when
compared to that with abiotic tests (0 mV vs Ag/AgCl) (Figure
S2a). The DC tests show that the polarization resistance (R
p
)
for biotic tests was 67 times lower compared to its abiotic
counterpart (Figure S2b), and corrosion rates (Figure S2c )
were 4 times higher. The EIS analysis also suggests that the
charge transfer resistance for biotic tests was 6 times lower
when compared to that of the abiotic tests (see Bode plots in
Figure S3a,b). The EIS analysis for the abiotic and biotic tests
indicates dierent sequences of corrosion mechanisms and
dierent electrical equivalent circuit (EEC) for each case
(Figure S3c,d).
Planktonic Tests: Passivation Eects of SL-hBN Coatings.
We conrmed the passive nature of SL-hBN coating against the
MIC eects of the planktonic cells in ve dierent ways, as
discussed below. First, we used potentiodynamic polarization
tests to observe the current response of the working electrode
after sweeping its applied potential away from the OCP
conditions. The nobler OCP value for the SL-hBN-Cu cell
(670 mV vs Ag/AgCl) when compared to that of bare copper
(735 mV vs Ag/AgCl) supports the passivation property of
the SL-hBN coating (Figure 3a). Lower current density in the
anodic branch indicates its higher corrosion resistance (Figure
3a). The single-layered hBN coating limits the corrosion
current to 6 mA/cm
2
, which is 4-fold lower compared to
that of bare Cu (27 mA/cm
2
)(Figure 3a). The anodic
polarization curve for the bare Cu is dominant at higher applied
potentials (starting from 0 V vs Ag/AgCl). Moreover, the
anodic branch for the bare Cu test registers a sharp increase in
current density (at 0 V vs Ag/AgCl), indicating the breakdown
of the passivation lm on the Cu surface and subsequent
copper dissolution. In contrast, the current density values for
the SL-hBN-Cu remain constant during the entire potential
range, conrming its ability to minimize copper dissolution
even at higher potential scans.
Second, we ran CV tests for the bare Cu and SL-hBN-Cu
cells for four consecutive cycles to investigate the underlying
mechanisms for the Cu corrosion. The CV results conrm that
the anodic current observed during the potential polarization
tests is due to Cu oxidation (Cu Cu
2+
+2e
). For example,
the CV test for the bare Cu cell yielded a sharp increase in the
current density when the potential approached +30 mV with an
oxidation peak at 144 mV vs Ag/AgCl (Figure 3b). This
oxidation peak can be attributed to Cu dissolution. The
reduction peak (40 mV vs Ag/AgCl) during the negative scan
corresponds to the reduction of Cu
2+
ions. Figure 3b provides
the evidence for the ability of the SL-hBN coating to suppress
the Cu dissolution. The peak anodic current (i
pa
) for the SL-
hBN coating (25 μA/cm
2
)is36 times lower compared to
that of bare Cu (915 μA/cm
2
). This anodic peak is absent for
the SL-hBN-Cu cell at positive potentials (0500 mV vs Ag/
AgCl).
Third, we used optical imaging to assess the degree of
corrosion attack on the underlying Cu surfaces after four cycles
of the CV runs. The CV test represents a destructive
electrochemical test. As shown in Figure 3c, the bare Cu
suered a higher degree of debilitation, whereas the SL-hBN-
coated Cu stayed intact even after the four CV runs.
Fourth, the post-mortem analysis revealed that the hBN
coatings minimized the degree of pitting attack on the
underlying Cu surface. We cleaned the surfaces of the corroded
specimens (i.e., after the CV runs) with 10% sulfuric acid to
remove remnants of the biolm and corrosion products. The
bare Cu sample was characterized by an extremely rough
surface with an abundant number of micropits throughout the
sample area, whereas the surface of the SL-hBN sample
remained intact, exhibiting only minor surface roughness and
isolated pits (Figure 3c).
Finally, EIS analysis was used to discern the protection
mechanism oered by SL-hBN coatings against the planktonic
cells. As shown in Figure 3d, the magnitude of the Nyquist arc
(i.e., polarization resistance (R
p
)) in the SL-hBN-Cu cell is 3-
fold higher than that of the bare Cu cell. The EEC tting
analysis conrms that the overall corrosion resistance in the SL-
hBN-Cu cell (R
corr
= charge transfer resistance (R
ct
) + pore
resistance (R
po
) = 52.78 kΩ·cm
2
)is49% higher than that of
the bare Cu (21.13 kΩ·cm
2
)(Table S1). The impedance
spectra in all cases follow a two-time constant model that is
connected in series with the solution resistance (R
s
)(Figure
S3d). The rst-time constant describes a pore resistance (R
po
),
which accounts for ionic or electron conductive pathways in
copper corrosion products or SL-hBN coating. The constant
phase element (Q
po
) d escribes the corresponding pore
capacitance and represents the ingress of aggressive electrolytes
into the porous layers of the coating present on the Cu surface.
The second-time constant describes the resistance to charge
transfer (R
ct
) between Cu and the electrolyte and the
capacitance due to double-layer phenomenon (C
dl
).
Biolm Tests: Microbial Corrosion Resistance of the SL-
hBN Coatings. We used the linear polarization resistance
method to investigate the eectiveness of the hBN coatings
against MIC of the biolm. At the end of day 24, the R
p
oered
by the SL-hBN coating (20463 Ω·cm
2
) was 9 times higher
than that of bare Cu (2373 Ω·cm
2
)(Figure 4a). Figure 4b
shows that the MIC rates in the SL-hBN cell were 67% lower
on day 1, 82% lower on day 15, and 87% lower on day 24.
The lower corrosion rates suggest the ability to minimize the
corrosion attack on the Cu surfaces. The corrosion current
(i
corr
) and corrosion rates were determined using the Stern-
Geary equation (eq 1).
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2246
=
i
B
R
corr
p
(1)
The values for the R
p
were determined from the slope of the
currentpotential curve at the open-circuit potential. The value
for the constant B was determined using eq 2.
ββ
ββ
=
+
B
2.3( )
ac
ac
(2)
The Tafel slopes for anodic (β
a
) and cathodic branches (β
c
)
were obtained from the Tafel plot. Finally, the corrosion rates
were calculated using eq 3.
ρ
=CR
Ki
A
(EW)
corr
(3)
where the constant K = 1.288 × 10
5
milli-inches was used to
obtain corrosion rates in milli-inches/year (mpy). EW, ρ, and A
are the equivalent weight (31.7 g), density (8.94 g/cm
3
), and
area (1 cm
2
) of the Cu specimen, respectively.
Barrier Properties of hBN Coatings. We used the EIS
test as a nonintrusive method for elucidating the reasons for the
MIC resistance of the SL-hBN coatings against eects of the
G20 biolm. The hBN coatings exert a dominant electro-
chemical polarization resistance to underlying corrosion
processes relative to the bare Cu cell (Figure 4c). The EEC
analysis conrms that the corrosion resistance (R
corr
)oered by
the hBN coatings ( 27.22 k Ω·cm
2
)is10 times higher than
that by the bare Cu cell (2.53 kΩ·cm
2
)(Table S2). The value
of the Q
po
for the SL-hBN coating was converted to interfacial
capacitance (C
c
) using the parallel resistance method developed
in an earlier study
32
and using the following equation
32,33
=
CR Q
nn
n
cp
(1 )/ 1/
(4)
where C
c
is the capacitance of coating lm, R
p
is the pore
resistance, and n is the exponent in the constant phase element.
The following ndings imply that the hBN coating oers
capacitive impedance behavior and provides a physical barrier
to stop aggressive metabolites (e.g.,H
2
SO
4
and HS
) from
contacting the Cu surface (Table S2).
13
The value of C
po
for
SL-hBN surface coating is an order of magnitude lower than
that of bare Cu. The value of C
dl
is also 3.4 times lower
(Table S2). These ndings indicate that the hBN coatings
reduce the surface roughness and minimize pathways that relay
ions into the underlying Cu surface.
34
The χ
2
test conrms an
excellent goodness of t between the measured and predicted
values for the EIS data (goodness of t=10
4
; average residual
<1%) (Figure S4). The compliance of the EIS data with the K
K relations is conrmed by the excellent goodness of t (10
3
using χ
2
value).
We used the R
corr
value obtained from the EIS analysis to
calculate the inhibition eciency using eq 5. The inhibition
eciency (IE%)
13
of the single-layered hBN coating was
determined to be as high as 91% (Table S2), which is on par
with a commercial coating such as polyaniline used in abiotic
environments (96%).
35
=
×
RR
R
IE
()
100
corr,coated corr,bare
corr,coated
(5)
The optical evidence further corroborates the barrier properties
of the hBN coatings against the MIC eects of the biolm
(Figure 5). Both the bare Cu and SL-hBN-Cu surface
developed identical biolm properties related to uniformity
and thicknesses (Figure 5a,c). However, the bare Cu surface
was characterized by an apparent layer of black corrosion
deposits (Figure 5a), whereas the SL-hBN-Cu surface remained
clean even after 24 days of the MIC experiment (Figure 5c).
Further, the underlying bare Cu surface suered from localized
attack by aggressive SRB metabolites (e.g., organic acids and
H
2
S), whereas the SL-hBN-Cu specimen faced only a minimal
degree of pitting (Figure 5b,d). As discussed below, the X-ray
diraction (XRD) results conrm that the SL-hBN coating
remained intact until the end of the MIC experiment. The SL-
hBN-coated Cu has also experienced a slight increase in the
corrosion rates during the linear polarization resistance tests
(Figure 4a,b), which is attributed to the defects in the CVD-
coated hBN coatings. Based on the ratio of R
ct
values for the
bare Cu and SL-hBN-Cu,
12
the percentage of the uncoated area
on the SL-hBN-Cu surface was estimated to be 9%.
These ndings demonstrate that the impermeable nature of
the SL-hBN coating prevents the sulfate reducing bacteria and
its aggressive metabolic products (acids, HS
) from contacting
the underlying Cu surface. The pore size of the 2D hBN (60
pm)
36
is smaller than the eective ionic radii (r) of a range of
participating redox species such as Cu
2+
(r = 73 pm) and Cu
+
(r
= 77 pm),
19
aggressive metabolites such as HS
(r = 207
pm),
37,38
and terminal electron acceptors such as hydronium
ion (H
3
O
+
)(r = 99 pm).
39
As explained in the subsequent
Figure 4. DC and AC corrosion tests establish microbial corrosion
resistance of SL-hBN coatings. (a) Polarization resistance data, (b)
corrosion rates, and (c) Nyquist plots for bare Cu and SL-hBN on
day 24.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2247
sections of this paper, the MIC resistance of the hBN coating is
also attributed to its insulating characteristics that disable the
cathodic reactions (e.g., proton reduction) and the subsequent
galvanic eects.
Signatures of Microbial Corrosion. At the end of the
MIC experiments, the corroded specimens were subjected to
visual tests and a series of SEM, energy-dispersive spectroscopy
(EDS), and XRD examinations to investigate the signatures of
the MIC attack. Both the bare Cu and SL-hBN-Cu electrodes
were characterized by thick and homogeneous biolms of rod-
shaped cells that is a typical characteristic of the D. alaskensis
G20 strain (Figure 6a,b). The visual tests revealed dominant,
dark-gray crystals in corrosion deposits representing chalcocite
(Cu
2
S), which is a signature of the MIC attack on Cu
surfaces.
7,40,41
The EDS analysis of the bare Cu and SL-hBN-
Cu surface shows the peaks for sulfur along with other elements
including C, Cu, O, and P (Figure 6c,d). We attribute the O
and C peaks to the carboxy (CO and CO) components of
extracellular polymeric (EPS) biolm.
7
The X-ray diractogram
of the bare Cu surface conrmed the presence of chalcocite
crystals (Figure 6e). The D. alaskensis G20 strain also aids in
formation of chalcocite and EPS compounds to develop a
defensive barrier against Cu toxicity.
7
The SL-hBN-Cu exhibits
a poor signal for the C peak. The intensity of the chalcolite
peak for the SL-hBN-Cu surface is also 3 orders of magnitude
lower compared to that of the bare Cu (Figure 6f). These
results suggest that D. alaskensis G20 uses copper as the
electron donor (eq 4) and the sulfate or proton as the electron
acceptor (eqs 68). It participates in a dissimilatory sulfate
reduction to generate corrosive hydrogen sulde (HS
) species
that is responsible for the MIC attack
42
(eqs 79). The lactate
is oxidized
43
throug h the lactate dehydrogenase enzyme
pathways to produce acetate (eq 11).
Anodic Oxidation
→+
+
eCu Cu 2
2
(6)
Cathodic Reduction (in the cytoplasm)
++→+ +
−+
e
S
O8H8HSOH3H
O
4
2
2
(7)
+→
+−
e
2
H2 H
2
(8)
++ +
−+
S
O4HHHS4H
O
4
2
22
(9)
Chalcocite Production
+→++
+−
2
Cu 2HS Cu S H S
2
22
2
(10)
++
→+++
−−+
−−
2
CH CHOHCOO SO 2H
2CH COO 2CO HS 2H
O
34
2
322
(11)
In light of the dissimilatory reduction mechanisms, the
following results conrm that the SL-hBN coating decelerates
the metabolic activity of SRB, associated production of biogenic
sulde, and subsequent MIC attack by D. alaskensis G20. The
high-performance liquid chromatography (HPLC) analysis
conrms the role of hBN coatings in suppressing the metabolic
activities. The electrolyte in the SL-hBN-Cu cell registered 2-
fold lower values for the organic acids (acetic acid and
propionic acid) when compared to the bare Cu cell (Figure
S5a). The SL-hBN-Cu cell has also registered lower values for
sulde (HS
) concentration throughout the temporal scale
(Figure S5b). For example, the HS
concentration for the SL-
hBN-Cu cell on day 7 (63 μg/L) was 1.4-fold lower than
that of the bare Cu cell (88 μg/L). The rate of increase in the
pH for the SL-hBN-Cu cell (7.2 to 7.8) was also lower than
that of the bare Cu cell (7.3 to 8.2) (Figure S5c). The lower
rate of pH decline indicates the ability of the hBN coatings to
retard one or all of the following: (i) conversion of sulfate (a
salt of strong acid) to sulde (a salt of weak base), (ii)
conversion of lactic acid (pK
a
= 3.86) to acetic acid (pK
a
4.76),
and (iii) proton binding by the suldes.
44
Galvanic Corrosion Eects of hBN Coatings Com-
pared with Those of Graphene and Bare Copper .
Galvanic corrosion occurs when two dissimilar metals are
coupled in a corrosive electrolyte. The metal with more positive
potential in a galvanic series will act as a cathode, and the metal
with negative potential acts as an anode. Corrosion occurs at
the interface of such galvanic couples. A coating such as
graphene (graphite) has more noble potential compared to
copper in a galvanic series.
45
A small defect such as pinhole,
cracks, or scratches in graphene coating will expose a small
anode (Cu) to large cathode (graphene), leading to a large
anodic current so as to balance the electron requirement of the
cathodic site. The areas with even such minor coating defects
are prone to localized corrosion, which will create a ripple eect
propagating it to other sites in the metal surface. In fact, recent
studies on galvanic eects of graphene described that grain
boundary defects in graphene coatings will accelerate localized
corrosion by forming galvanic couples.
4548
To study and compare the galvanic eects of graphene and
hBN coatings with bare copper, we carried out galvanic
corrosion tests using the ASTM G 71-81 standards. These tests
were carried out by conguring the Gamry potentiostat in a
zero-resistance ammeter mode with transferred single-layer
graphene and SL-hBN lms on a SiO
2
/Si wafer as cathode, bare
Cu as anode, and the dened lactate C medium along with the
planktonic cells of Desulfovibrio alaskensis G20 as the electro-
Figure 5. Optical images of bare Cu and SL-hBN-Cu after 12 days
of MIC experiment. Corroded bare copper (a) before and (b) after
cleaning. MIC-resistant SL-hBN-Cu (c) before and (d) after
cleaning. Scale bar: 200 μm.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2248
lyte. The procedures for transferring the SLG and SL-hBN lms
on a SiO
2
/Si wafer are depicted in Figure S6. Figure S7 shows
the optical images of the transferred SLG and SL-hBN lms
onto SiO
2
/Si wafer. Figure 7 shows a three-electrode galvanic
corrosion cell (details in the Methods section) used in this
study. SiO
2
/Si was used as a control specimen to compare the
galvanic current obtained from Cu/SLG and Cu/SL-hBN
couples. The galvanic corrosion test was carried out within 24 h
of the exposure to Desulfovibrio alaskensis G20 lactate C
medium with a stable value for the open-circuit potential.
Figure 8a shows that the galvanic current density (I
g
) for Cu/
SLG (32.9 μA/cm
2
)is392 times higher compared to that
for Cu/SL-hBN (8.4 × 10
2
μA/cm
2
). The higher galvanic
current density is directly proportional to higher corrosion rate.
The lower galvanic current density in Cu/SL-hBN when
compared to that of Cu/SLG clearly demonstrates that hBN
coatings are far less vulnerable to galvanic corrosion eects. In
fact, the galvanic current and galvanic corrosion rate of the SL-
Figure 6. Microbial corrosion signatures. SEM images of G20 biolm formed on (a) bare Cu and (b) SL-hBN-Cu after 12 days of microbial
corrosion experiment. EDS data shows sulfur peaks for (c) bare Cu and (b) SL-hBN. XRD data showing formation of chalcolite compounds
on the surfaces of (e) bare Cu and (f) SL-hBN-Cu.
Figure 7. Corrosion cell for galvanic current a nd potential
measurement.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2249
hBN are comparable to those of an insulating SiO
2
/Si surface
(Table 1), indicating its outstanding insulating characteristics.
The galvanic current density was converted to corrosion rates
in mills per year (Table 1 ) using the Faradays law as described
by procedure ASTM G102.
ρ
=
××KI
corrosion rate (mpy)
EW
1g
where K
1
is the Faraday constant (0.1288, mpy), I
g
is galvanic
corrosion density in μA/cm
2
, EW is the equivalent weight of
copper (31.7), and ρ is copper density (8.94 g/cm
3
).
The signicantly higher galvanic corrosion rates in the case of
Cu/SLG clearly demonstrates that graphene coating on copper
leads to galvanic problems. The electrode potential from the
galvanic couples can be used to determine the higher
cathodic nature of the metal.
45
The more positive the value of
potential in the galvanic couple, the higher its cathodic nature.
From Figure 8b, galvanic potential of Cu/SLG is higher (744
mV) than that of Cu/SL-hBN (792 mV), which we expect is
related to the dierences in electrical conductivity of SLG and
SL-hBN. Moreover, the galvanic potential of SL-hBN is
comparable to that of an insulating SiO
2
/Si surface (Figure
8b). Since graphene acts more cathodic when coupled to
copper than hBN, Cu/SLG couple generates higher anodic
current, leading to greater extent of galvanic corrosion. This is
the reason why SL-hBN coatings reduce the galvanic corrosion
eects by 400 times when compared to SLG coatings, as
revealed in our experiments. It should be noted that the
electron mobility of hBN (4923 cm
2
/Vs)
49
is 154-fold
lower than that of copper (32 cm
2
/Vs)
50
and 40 times
lower than that in graphene (2 × 10
5
cm
2
/Vs).
51
The
insulating behavior of hBN is due to the dierences in
electronegativity between the boron and nitrogen atoms, which
results in localization of π-electrons around the nitrogen
atoms.
52
CONCLUSION
This study demonstrates the ability of single-layered hBN to
passivate the negative eects of microbially induced corrosion.
It is the thinnest insulating coating that combats the corroding
eects of the aggressive metabolit es generated by the
dissimilatory sulfate reduction process. The MIC resistance of
the single-layered hBN coating emerges from the combined
eects of its impermeable nature (barrier for electron acceptors,
redox species, and biogenic chemicals) and insulating character-
istics (suppresses cathodic reduction and galvanic eects).
METHODS
A complete description of the experimental procedures can be found
in the Supporting Information, and only a brief account is given below.
The copper foils were coated with single-layer hexagonal boron nitride
(CVD-2X1-BN; 20 μm thick; Graphene Supermarket) via chemical
vapor deposition using the earlier procedures dened in the
literature.
53,54
D. alaskensis was anaerobically grown in the lactate C
medium using the procedures described previously.
55,56
Microbial
corrosion experiments were carried out in a 400 mL single-
compartment corrosion cell consisting of three electrodes: a graphite
plate as a counter electrode, a Ag/AgCl as a reference electrode, and a
working electrode area of 1 cm
2
. We carried out abiotic tests,
planktonic cell tests, and biolm tests as described in the Supporting
Information.
Cyclic voltammetry, linear polarization resistance, potentiodynamic
polarization, and electrochemical impedance spectroscopy were used
to analyze the resistance of the coatings against MIC conditions. The
procedures reported previously
57
were used to transfer the SL-hBN
coatings from an underlying copper foil to the SiO
2
/Si substrate. The
samples were a nalyzed us ing SEM, TEM, XRD, and Raman
spectroscopy. To determine the organic, inorganic, anions, and
metal ions, we collected the samples of the electrolyte from the test
cells periodically using a sterile syringe lter with a pore diameter of
0.2 μm. Concentration of organic acids (lactic, acetic, and propionic
acid) was determined using a Shimadzu HPLC equipped with an
Aminex HPX-87H column (300 mm × 7.8 mm dimension), an SPD-
10A (UVvis) detector, and 0.005 M H
2
SO
4
as the mobile phase.
Concentration of aqueous sulde was determined using a spectropho-
tometer following the USEPA methylene blue method.
58
The pH of
the electrolyte samples was measured using an Orion Star Benchtop
pH meter.
ASSOCIATED CONTENT
*
S
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsnano.7b06211.
Detailed methods section, gures (electrochemical tests
for bare Cu foil in sterile and D. alaskensis media; tted
data for Nyquist plot for bare Cu, SL-hBN; organic acid
concentration, sulde and pH measurements for bare-
Cu-cell and SL-hBN-cell ; temporal proles of R
ct
, pore
and double layer capacitance), tables (electrical equiv-
alent circuit parameters for Nyquist plot conducted in
planktonic medium for bare Cu and SL-hBN-Cu; EEC
Figure 8. Temporal variation of (a) galvanic current I
g
(μA/cm
2
)
and (b) galvanic potential (mV) for galvanic couples: Cu/SiO
2
/Si,
Cu/SLG and Cu/SL-hBN in Desulfovibrio alaskensis G20 lactate C
medium. Cu is used as anode and SiO
2
/Si, SLG, and SL-hBN as
cathode. The anode to cathode area ratios for all the galvanic
couples are maintained at 1.7.
Table 1. Galvanic Corrosion Rates Based on Galvanic
Couple Current Density
galvanic
couple
galvanic current density
(μA/cm
2
)
galvanic corrosion rate
(mpy)
Cu/SiO
2
/Si 6.22 × 10
3
2.8 × 10
3
Cu/SLG 32.9 14.8
Cu/SL-hBN 8.4 × 10
2
3.79 × 10
2
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2250
parameters for Nyquist plot conducted in sessile medium
for bare Cu and SL-hBN-Cu), and references for the
methods section (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: venkata.gadhamshetty@sdsmt.edu.
ORCID
Nikhil A. Koratkar: 0000-0002-4080-3786
Venkataramana Gadhamshetty: 0000-0002-8418-3515
Notes
The authors declare no competing nancial interest.
ACKNOWLEDGMENTS
Funding support from National Science Foundation CAREER
Award (#1454102), National Aeronautics and Space Admin-
istration (NNX16AQ98A), and the South Dakota Board of
Regents u nder the auspices of the Surface Engineering
Research Center (SERC) is acknowledged.
REFERENCES
(1) Krishnamurthy, A.; Gadhamshetty, V.; Mukherjee, R.; Natarajan,
B.; Eksik, O.; Shojaee, S. A.; Lucca, D. A.; Ren, W.; Cheng, H.-M.;
Koratkar, N. Superiority of Graphene over Polymer Coatings for
Prevention of Microbially Induced Corrosion. Sci. Rep. 2015, 5, 13858.
(2) Heitz, E.; Flemming, H.-C.; Sand, W. Microbially Inuenced
Corrosion of Materials: Scientic and Engineering Aspects; Springer-
Verlag: Heidelberg, 1996; p 475.
(3) Zhang, D.; Qian, H.; Xiao, K.; Zhou, F.; Liu, Z.; Li, X. Corrosion
Inhibition of 304 Stainless Steel by Paecilomyces Variotii and Aspergillus
Niger in Aqueous Environment. Corros. Eng., Sci. Technol. 2016, 51,
285290.
(4) Enzien, M.; Wu, M.; Frank, J.; Pope, D. Nonbiocidal Control of
Microbiologically Inuenced Corrosion Using Organic Film-Forming
Inhibitors. Proceedings of the National Association of Corrosion Engineers,
4th ed; NACE International, 1996.
(5) Rajasekar, A. Biodegradation of Petroleum Hydrocarbon and Its
Inuence on Corrosion with Special Reference to Petroleum Industry.
In Biodegradation and Bioconversion of Hydrocarbons; Heimann, K.,
Karthikeyan, O. P., Muthu, S. S., Eds.; Springer Nature: Singapore,
2017; p 311.
(6) Zuo, R.; O
̈
rnek, D.; Syrett, B.; Green, R.; Hsu, C.-H.; Mansfeld,
F.; Wood, T. Inhibiting Mild Steel Corrosion from Sulfate-Reducing
Bacteria Using Antimicrobial-Producing Biofilms in Three-Mile-Island
Process Water. Appl. Microbiol. Biotechnol. 2004, 64, 275283.
(7) Chen, S.; Wang, P.; Zhang, D. Corrosion Behavior of Copper
Under Biofilm of Sulfate-Reducing Bacteria. Corros. Sci. 2014, 87,
407415.
(8) Chilkoor, G.; Upadhyayula, V. K.; Gadhamshetty, V.; Koratkar,
N.; Tysklind, M. Sustainability of Renewable Fuel Infrastructure: A
Screening LCA Case Study of Anticorrosive Graphene Oxide Epoxy
Liners in Steel Tanks for the Storage of Biodiesel and its Blends.
Environ. Sci.: Processes Impacts 2017, 19, 141153.
(9) Donoghue, M. O.; Graham, R. G.; Datta, V. W.; Garrett, R. W.;
Garrett, J. W. Field Performance versus Laboratory Testing: A Study of
Epoxy Tank and Vessel Linings Used in the Canadian Oil Patch. In
Corrosion 2003; NACE International: San Diego, CA, 2003.
(10) Heyer, A. Microbiologically Inuenced Corrosion in Ship Ballast
Tanks. Ph.D. Dissertation, Delft University of Technology, Delft,
Netherlands, 2013.
(11) Tambe, S.; Jagtap, S.; Chaurasiya, A.; Joshi, K. K. Evaluation of
Microbial Corrosion of Epoxy Coating by Using Sulphate Reducing
Bacteria. Prog. Org. Coat. 2016, 94,49
55.
(12) Prasai, D.; Tuberquia, J. C.; Harl, R. R.; Jennings, G. K.; Bolotin,
K. I. Graphene: Corrosion-Inhibiting Coating. ACS Nano 2012, 6,
11021108.
(13) Huh, J.-H.; Kim, S. H.; Chu, J. H.; Kim, S. Y.; Kim, J. H.; Kwon,
S.-Y. Enhancement of Seawater Corrosion Resistance in Copper Using
Acetone-Derived Graphene Coating. Nanoscale 2014, 6, 43794386.
(14) Raman, R. S.; Banerjee, P. C.; Lobo, D. E.; Gullapalli, H.;
Sumandasa, M.; Kumar, A.; Choudhary, L.; Tkacz, R.; Ajayan, P. M.;
Majumder, M. Protecting Copper from Electrochemical Degradation
by Graphene Coating. Carbon 2012, 50, 40404045.
(15) Krishnamurthy, A.; Gadhamshetty, V.; Mukherjee, R.; Chen, Z.;
Ren, W.; Cheng, H.-M.; Koratkar, N. Passivation of Microbial
Corrosion Using a Graphene Coating. Carbon 2013, 56,4549.
(16) Upadhyayula, V. K.; Meyer, D. E.; Gadhamshetty, V.; Koratkar,
N. Screening-Level Life Cycle Assessment of Graphene-Poly (ether
imide) Coatings Protecting Unalloyed Steel from Severe Atmospheric
Corrosion. ACS Sustainable Chem. Eng. 2017, 5, 26562667.
(17) Dennis, R. V.; Viyannalage, L. T.; Gaikwad, A. V.; Rout, T. K.;
Banerjee, S. Graphene Nanocomposite Coatings for Protecting Low-
Alloy Steels from Corrosion. Am. Ceram. Soc. Bull. 2013, 92,1824.
(18) Mahvash, F.; Eissa, S.; Bordjiba, T.; Tavares, A.; Szkopek, T.;
Siaj, M. Corrosion Resistance of Monolayer Hexagonal Boron Nitride
on Copper. Sci. Rep. 2017, 7, 42139.
(19) Parra, C.; Montero-Silva, F.; Henríquez, R.; Flores, M.; Garín,
C.; Ramírez, C.; Moreno, M.; Correa, J.; Seeger, M.; Ha
̈
berle, P.
Suppressing Bacterial Interaction with Copper Surfaces through
Graphene and Hexagonal-Boron Nitride Coatings. ACS Appl. Mater.
Interfaces 2015, 7, 64306437.
(20) Shen, L.; Zhao, Y.; Wang, Y.; Song, R.; Yao, Q.; Chen, S.; Chai,
Y. A Long-Term Corrosion Barrier with an Insulating Boron Nitride
Monolayer. J. Mater. Chem. A 2016, 4, 50445050.
(21) Kim, G.; Kim, M.; Hyun, C.; Hong, S.; Ma, K. Y.; Shin, H. S.;
Lim, H. Hexagonal Boron Nitride/Au Substrate for Manipulating
Surface Plasmon and Enhancing Capability of Surface-Enhanced
Raman Spectroscopy. ACS Nano 2016
, 10, 1115611162.
(22) Liu, Z.; Gong, Y.; Zhou, W.; Ma, L.; Yu, J.; Idrobo, J. C.; Jung, J.;
MacDonald, A. H.; Vajtai, R.; Lou, J.; et al. Ultrathin High-
Temperature Oxidation-Resistant Coa tings of Hexagonal Boron
Nitride. Nat. Commun. 2013, 4, 2541.
(23) Husain, E.; Narayanan, T. N.; Taha-Tijerina, J. J.; Vinod, S.;
Vajtai, R.; Ajayan, P. M. Marine Corrosion Protective Coatings of
Hexagonal Boron Nitride Thin Films on Stainless Steel. ACS Appl.
Mater. Interfaces 2013, 5, 41294135.
(24) Zhang, J.; Yang, Y.; Lou, J. Investigation of Hexagonal Boron
Nitride as an Atomically Thin Corrosion Passivation Coating in
Aqueous Solution. Nanotechnology 2016, 27, 364004.
(25) Lin, Y.; Williams, T. V.; Connell, J. W. Soluble, Exfoliated
Hexagonal Boron Nitride Nanosheets. J. Phys. Chem. Lett. 2010, 1,
277283.
(26) Gorbachev, R. V.; Riaz, I.; Nair, R. R.; Jalil, R.; Britnell, L.; Belle,
B. D.; Hill, E. W.; Novoselov, K. S.; Watanabe, K.; Taniguchi, T.; et al.
Hunting for Monolayer Boron Nitride: Optical and Raman Signatures.
Small 2011, 7, 465468.
(27) Wlasny, I.; Dabrowski, P.; Rogala, M.; Kowalczyk, P.; Pasternak,
I.; Strupinski, W.; Baranowski, J.; Klusek, Z. Role of Graphene Defects
in Corrosion of Graphene-Coated Cu (111) Surface. Appl. Phys. Lett.
2013, 102, 111601.
(28) Wlasny, I.; Dabrowski, P.; Rogala, M.; Pasternak, I.; Strupinski,
W.; Baranowski, J.; Klusek, Z. Impact of Electrolyte Intercalation on
the Corrosion of Graphene-Coated Copper. Corros. Sci. 2015, 92,69
75.
(29) Chow, P. K.; Singh, E.; Viana, B. C.; Gao, J.; Luo, J.; Li, J.; Lin,
Z.; Elías, A. L.; Shi, Y.; Wang, Z.; et al. Wetting of Mono and Few-
layered WS2 and MoS2 Films Supported on Si/SiO2 Substrates. ACS
Nano 2015, 9, 30233031.
(30) Hu, B.; Ago, H.; Ito, Y.; Kawahara, K.; Tsuji, M.; Magome, E.;
Sumitani, K.; Mizuta, N.; Ikeda, K.-i.; Mizuno, S. Epitaxial Growth of
Large-Area Single-Layer Graphene Over Cu (111)/Sapphire by
Atmospheric Pressure CVD. Carbon 2012, 50,5765.
(31) Song, X.; Gao, J.; Gao, T.; Nie, Y.; Sun, J.; Chen, Y.; Jin, C.;
Ding, F.; Zhang, Y.; Liu, Z. Wafer-scale CVD Growth of Monolayer
Hexagonal Boron Nitride with Large Domain Size by Cu Foil
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2251
Enclosure Approach; https://arxiv.org/abs/1501.01740 (accessed
August 10, 2017).
(32) Brug, G.; Van Den Eeden, A.; Sluyters-Rehbach, M.; Sluyters, J.
The Analysis of Electrode Impedances Complicated by the Presence of
a Constant Phase Element. J. Electroanal. Chem. Interfacial Electrochem.
1984, 176, 275295.
(33) Aneja, K. S.; Bo
̈
hm, H. M.; Khanna, A.; Bo
̈
hm, S. Functionalised
Graphene as a Barrier Against Corrosion. FlatChem. 2017, 1,1119.
(34) Schmidt, E.; Shi, S.; Ruden, P. P.; Frisbie, C. D. Characterization
of the Electric Double Layer Formation Dynamics of a Metal/Ionic
Liquid/Metal Structure. ACS Appl. Mater. Interfaces 2016, 8, 14879
14884.
(35) Shabani-Nooshabadi, M.; Mollahoseiny, M.; Jafari, Y. Electro-
polymerized Coatings of Polyaniline on Copper by Using the
Galvanostatic Method and their Corrosion Protection Performance
in HCl Medium. Surf. Interface Anal. 2014, 46, 472479.
(36) Yan, K.; Lee, H.-W.; Gao, T.; Zheng, G.; Yao, H.; Wang, H.; Lu,
Z.; Zhou, Y.; Liang, Z.; Liu, Z.; et al. Ultrathin Two-Dimensional
Atomic Crystals as Stable Interfacial Layer for Improvement of
Lithium Metal Anode. Nano Lett. 2014, 14, 60166022.
(37) Dasent, W. E. Inorganic Energetics: An Introduction; Cambridge
University Press: Cambridge, 1982; p 78.
(38) Jenkins, H.; Thakur, K. Reappraisal of Thermochemical Radii
for Complex Ions. J. Chem. Educ. 1979, 56, 576.
(39) Barrett, J. Inorganic Chemistry in Aqueous Solution; The Royal
Society of Chemistry: Cambridge, 2003; p 35.
(40) McNeil, M.; Jones, J.; Little, B. Production of Sulfide Minerals
by Sulfate-Reducing Bacteria during Microbiologically Influenced
Corrosion of Copper. Corrosion 1991, 47, 674677.
(41) Geesey, G. G.; Lewandowski, Z.; Flemming, H.-C. Biofouling
and Biocorrosion in Industrial Water Systems; CRC Press: Boca Raton,
FL, 1994; p 214.
(42) Keller, K. L.; Rapp-Giles, B. J.; Semkiw, E. S.; Porat, I.; Brown, S.
D.; Wall, J. D. New Model for Electron Flow for Sulfate Reduction in
Desulfovibrio Alaskensis G20. Appl. Environ. Microbiol. 2014, 80, 855
868.
(43) Lee, A. K.; Buehler, M. G.; Newman, D. K. Influence of a Dual-
Species Biofilm on the Corrosion of Mild Steel. Corros. Sci. 2006
, 48,
165178.
(44) Wikieł , A. J.; Datsenko, I.; Vera, M.; Sand, W. Impact of
Desulfovibrio Alaskensis Biofilms on Corrosion Behaviour of Carbon
Steel in Marine Environment. Bioelectrochemistry 2014, 97,5260.
(45) Cui, C.; Lim, A. T. O.; Huang, J. A Cautionary Note on
Graphene Anti-Corrosion Coatings. Nat. Nanotechnol. 2017, 12, 834.
(46) Schriver, M.; Regan, W.; Gannett, W. J.; Zaniewski, A. M.;
Crommie, M. F.; Zettl, A. Graphene as a Long-Term Metal Oxidation
Barrier: Worse than Nothing. ACS Nano 2013, 7, 57635768.
(47) Zhou, F.; Li, Z.; Shenoy, G. J.; Li, L.; Liu, H. Enhanced Room-
Temperature Corrosion of Copper in the Presence of Graphene. ACS
Nano 2013, 7, 69396947.
(48) Datta, D.; Li, J.; Koratkar, N.; Shenoy, V. B. Enhanced Lithiation
in Defective Graphene. Carbon 2014, 80, 305310.
(49) Park, H.; Kim, T. K.; Cho, S. W.; Jang, H. S.; Lee, S. I.; Choi, S.-
Y. Large-Scale Synthesis of Uniform Hexagonal Boron Nitride Films
by Plasma-Enhanced Atomic Layer Deposition. Sci. Rep. 2017, 7,
40091.
(50) Fulay, P.; Lee, J.-K. Electronic, Magnetic, and Optical Materials;
CRC Press: Boca Raton, FL, 2016; p 56.
(51) Tan, H.; Wang, D.; Guo, Y. Thermal Growth of Graphene: A
Review. Coatings 2018, 8, 40.
(52) Hod, O. Graphite and hexagonal Boron-Nitride have the Same
Interlayer Distance. Why? J. Chem. Theory Comput. 2012, 8, 1360
1369.
(53) Kim, K. K.; Hsu, A.; Jia, X.; Kim, S. M.; Shi, Y.; Hofmann, M.;
Nezich, D.; Rodriguez-Nieva, J. F.; Dresselhaus, M.; Palacios, T.; et al.
Synthesis of Monolayer Hexagonal Boron Nitride on Cu Foil Using
Chemical Vapor Deposition. Nano Lett. 2012, 12, 161166.
(54) Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.; Piner, R.;
Velamakanni, A.; Jung, I.; Tutuc, E.; et al. Large-Area Synthesis of
High-Quality and Uniform Graphene Films on Copper Foils. Science
2009, 324, 1312
1314.
(55) Sani, R. K.; Geesey, G.; Peyton, B. M. Assessment of Lead
Toxicity to Desulfovibrio desulfuricans G20: Influence of Components
of Lactate C Medium. Adv. Environ. Res. 2001, 5, 269276.
(56) Burlage, R. S.; Atlas, R.; Stahl, D.; Geesey, G.; Sayler, G.
Techniques in Microbial Ecology; Oxford University Press: New York,
1998; pp 4243.
(57) Kim, K. K.; Hsu, A.; Jia, X.; Kim, S. M.; Shi, Y.; Dresselhaus, M.;
Palacios, T.; Kong, J. Synthesis and Characterization of Hexagonal
Boron Nitride Film as a Dielectric Layer for Graphene Devices. ACS
Nano 2012, 6, 85838590.
(58) Nielsen, A. H.; Vollertsen, J.; Hvitved-Jacobsen, T. Determi-
nation of Kinetics and Stoichiometry of Chemical Sulfide Oxidation in
Wastewater of Sewer Networks. Environ. Sci. Technol. 2003, 37, 3853
3858.
ACS Nano Article
DOI: 10.1021/acsnano.7b06211
ACS Nano 2018, 12, 22422252
2252